The present invention relates to a copper alloy suitable for a lead frame material, a terminal and/or connector material, a switch material, or the like, processed in a desired shape through a process including a punching step. Further the present invention relates to a method for manufacturing the copper alloy.
Conventionally, a copper-series material with excellent electric and thermal conductivity, as well as iron-series material, is frequently employed for a lead frame material or a terminal material. Such a copper-series material is also employed for a semiconductor device member, whose heat radiation property has been important in accordance with the advancement of high integration and miniaturization of the semiconductor member.
When a copper-series material is used for a lead frame, the material must have excellent plating properties for precious metal (such as Ag or Pd) or solder, and surface smoothness, as well as electric and thermal conductivity.
Although a variety of lead frame copper alloys were developed to meet such requirements in the past, not many such copper alloys were satisfactory. Thus, only several types of the alloys are employed now. Among them, a Cuxe2x80x94Crxe2x80x94Sn-series alloy is recognized as being compatible with high conductivity and high mechanical strength, so that it is one of the most frequently used alloys.
In the meantime, although a punching method or etching method is generally applied for lead frame mold processing, the punching method is frequently used from the standpoint of productivity.
However, with respect to the conventional Cuxe2x80x94Crxe2x80x94Sn-series alloy, burring or generation of processing powder occurs during punching, that causes short-circuiting between leads or reduced dimensional precision of a lead frame. If burring occurs, the metal die maintenance cycle is made short, and the manufacturing cost increases. In particular, these problems are significant in a multi-pin type lead frame.
For a lead frame manufacturer, low-cost lead frames are demanded according to the fast-grow of semiconductor industry. Thus, they are important tasks how the rate of operation of punching facilities is raised, and how punch faults are decreased and product yields are increased. In particular, in the lead frame made of the Cuxe2x80x94Crxe2x80x94Sn-series alloy, with its demand increased, significant improvement of punchability (punching processability) is strongly desired.
(1) A copper alloy with excellent punchability, comprising 0.2 to 0.35 wt % of Cr, 0.1 to 0.5 wt % of Sn, and 0.1 to 0.5 wt % of Zn, the balance being made of Cu and unavoidable impurities, wherein, in a Cu matrix, a precipitation phase A of Cr or a Cr compound of 0.1 to 10 xcexcm in maximum diameter, is provided, at a density in number of 1xc3x97103 to 3xc3x97105/mm2, and a precipitation phase B of Cr or a Cr compound of 0.001 to 0.030 xcexcm in maximum diameter, is provided, at a density in number that is 10 times or more of that of the precipitation phase A (hereinafter, this copper alloy is referred to as a first embodiment of the present invention).
(2) A copper alloy with excellent punchability, comprising 0.2 to 0.35 wt % of Cr, 0.1 to 0.5 wt % of Sn, and 0.1 to 0.5 wt % of Zn, and further comprising at least one selected from the group consisting of 0.001 to 0.06 wt % of Pb, 0.001 to 0.06 wt % of Bi, 0.005 to 0.1 wt % of Ca, 0.005 to 0.1 wt % of Sr, 0.005 to 0.1 wt % of Te, 0.005 to 0.1 wt % of Se, and 0.005 to 0.1 wt % of a rare earth element, in a total amount of 0.001 to 0.1 wt %, the balance being made of Cu and unavoidable impurities, wherein, in a Cu matrix, a precipitation phase A of Cr or a Cr compound of 0.1 to 10 xcexcm in maximum diameter, is provided, at a density in number of 1xc3x97103 to 3xc3x97105/mm2, and a precipitation phase B of Cr or a Cr compound of 0.001 to 0.030 xcexcm in maximum diameter, is provided, at a density in number that is 10 times or more of that of the precipitation phase A (hereinafter, this copper alloy is referred to as a second embodiment of the present invention).
(3) A copper alloy with excellent punchability, comprising 0.2 to 0.35 wt % of Cr, 0.1 to 0.5 wt % of Sn, 0.1 to 0.5 wt % of Zn, and 0.005 to 0.1 wt % of Si, the balance being made of Cu and unavoidable impurities, wherein, in a Cu matrix, a precipitation phase A of Cr or a Cr compound of 0.1 to 10 xcexcm in maximum diameter, is provided, at a density in number of 1xc3x97103 to 3xc3x97105/mm2, and a precipitation phase B of Cr or a Cr compound of 0.001 to 0.030 xcexcm in maximum diameter, is provided, at a density in number that is 10 times or more of that of the precipitation phase A (hereinafter, this copper alloy is referred to as a third embodiment of the present invention).
(4) A copper alloy with excellent punchability, comprising 0.2 to 0.35 wt % of Cr, 0.1 to 0.5 wt % of Sn, 0.1 to 0.5 wt % of Zn, 0.005 to 0.1 wt % of Si, and further comprising at least one selected from the group consisting of 0.001 to 0.06 wt % of Pb, 0.001 to 0.06 wt % of Bi, 0.005 to 0.1 wt % of Ca, 0.005 to 0.1 wt % of Sr, 0.005 to 0.1 wt % of Te, 0.005 to 0.1 wt % of Se, and 0.005 to 0.1 wt % of a rare earth element, in a total amount of 0.001 to 0.1 wt %, the balance being made of Cu and unavoidable impurities, wherein, in a Cu matrix, a precipitation phase A of Cr or a Cr compound of 0.1 to 10 xcexcm in maximum diameter, is provided, at a density in number of 1xc3x97103 to 3xc3x97105/mm2, and a precipitation phase B of Cr or a Cr compound of 0.001 to 0.030 xcexcm in maximum diameter, is provided, at a density in number that is 10 times or more of that of the precipitation phase A (hereinafter, this copper alloy is referred to as a fourth embodiment of the present invention).
(5) A method of manufacturing a copper alloy with excellent punchability as stated in any one of the above (1) to (4), by subjecting the copper alloy at least to a hot working and a cold working, wherein heat treatment is applied at a temperature of 880 to 980xc2x0 C. before the hot working, and aging treatment is applied at a temperature of 360 to 470xc2x0 C. before or after the cold working.
Although the present invention relates to a copper alloy particularly suitable for a lead frame material, it is applicable to general materials manufactured in a process containing punching, such as a terminal material used for automobiles or a connector material used for commercially available equipment.
The copper alloy of the present invention is primarily characterized in that, in a Cu matrix, there coexist a precipitation phase A of coarse Cr or a Cr component of 0.1 to 10 xcexcm in maximum diameter, for improving punchability, and a precipitation phase B of fine Cr or a Cr compound of 0.001 to 0.030 xcexcm (1 nm to 30 nm) in maximum diameter, for ensuring mechanical strength. The maximum diameter referred to here means the diameter of a sphere when a precipitation phase is spherical; a long diameter when the phase is elliptical; and the maximum length when the phase is bar-shaped.
The inventors conducted research for a copper alloy-series and found out that an ideal precipitation state of Cr or a Cr compound can be achieved by specific amount of components and definition of manufacturing conditions, to obtain a copper alloy with excellent practicality.
The copper alloy of the present invention is preferably manufactured by subjecting it to heat treatment at 880 to 980xc2x0 C. before hot working, to precipitate coarse Cr or a Cr compound, and further subjecting it to aging treatment at 360 to 470xc2x0 C., to precipitate fine Cr or a Cr compound.
Now, reasons for defining alloy components of a copper alloy according to the present invention will be described.
Conventionally, when Cr was added into Cu, only precipitation and hardening of Cr were expected. The size of each of the precipitation phases of Cr or a Cr compound dispersing in the Cu matrix, was 0.001 to 0.030 xcexcm in maximum diameter, and almost no coarse precipitation phase of 0.1 to 10 xcexcm in maximum diameter was existed.
The present invention has been made by finding out that to attain improved advantageous effect both on punchability, and precipitation and hardening, and thus, it is required to define Cr component to a specific range.
In the present invention, if an amount of Cr is less than 0.2 wt %, even if heat treatment before hot working is carried out at 980xc2x0 C., almost no coarse precipitation phase A precipitates, and thus, punchability is not improved. Conversely, if an amount of Cr exceeds 0.35 wt %, Cr is produced as a crystallized material during casting solidification. This crystallized Cr can be a starting point of breaking during punching process, and thus it can be effective for punching. However, the Cr disperses sparsely due to the nature of a crystallized material, and its size tends to be coarse (greater than 10 xcexcm). That is, even if Cr is added in excess of 0.35 wt %, an advantageous effect proportional to an addition amount cannot be obtained. In addition, a crystallized Cr material of size exceeding 10 xcexcm is inadequate, in that abrasion of tools is accelerated, and the service life of a metal die is made short.
From the above viewpoint, the amount of the content of Cr was defined to be 0.2 to 0.35 wt %.
As described above, the present invention is mainly characterized in that a coarse precipitation phase A of Cr or a Cr compound, and a fine precipitation phase B, coexist.
As the coarse precipitation phase A in the present invention improves punchability as a starting point of breaking, a precipitation phase of less than 0.1 xcexcm in maximum diameter cannot be a starting point of breaking. Thus, the improvement of punchability, which is an object of the present invention, cannot be achieved. Conversely, a precipitation phase of more than 10 xcexcm in maximum diameter is not preferable, because the life of a punching metal die is reduced. Therefore, a state, in which a precipitation phase A of 0.1 to 10 xcexcm in maximum diameter disperses in proper quantity, is ideal.
If the density in number of the coarse precipitation phase A is less than 1xc3x97103/mm2, the punchability is not improved. If 3xc3x97105/mm2 is exceeded, the precipitation phase B decreases, with an increase of the precipitation phase A, and the strength characteristics are lowered. Therefore, the density in number of the precipitation phase A is set to be 1xc3x97103 to 3xc3x97105/mm2.
On the other hand, a fine precipitation phase B, which precipitates at the nanometer level, improves strength characteristics. The required strength characteristics cannot be obtained unless the density in number of the precipitation phase B is at least 10 times or more of that of the precipitation phase A. If the fine precipitation phase B increases excessively in quantity, the density in number of the coarse precipitation phase A, which improves punchability, is lowered. Therefore, the density in number of the precipitation phase B may be set suitably so as to attain sufficient strength characteristics and punchability.
The present invention relates to a copper alloy with improved punchability by limiting the size and density in number of each of the precipitation phase A of Cr or a Cr compound, and the precipitation phase B, as well as the content of Cr.
Sn has an advantageous effect on enhancing the material strength characteristics. If its content is less than 0.1 wt %, the advantageous effect cannot be sufficiently obtained. If 0.5 wt % is exceeded, the conductivity is significantly lowered. Therefore, the contents of Sn range from 0.1 to 0.5 wt %.
Zn has an advantageous effect of improving resistance to peeling of solder or plating under heat of Sn plating or solder plating, and migration resistance. In particular, when Zn is used as a lead frame or a terminal, the degradation of a soldering portion after mounting with time is important. Thus, the addition of Zn is indispensable. If its content is less than 0.1 wt %, a sufficient advantageous effect cannot be achieved. Conversely, if the content exceeds 0.5 wt %, an advantageous effect proportional to such quantity added cannot be achieved, and in addition, the conductivity is lowered. Therefore, the contents of Zn range from 0.1 to 0.5 wt %.
Pb, Bi, Ca, Sr, Te, Se, and a rare earth element, such as Sc, Y, or La, can be added to improve punchability. These elements have small solid solubility into the Cu matrix and they are dispersed in the Cu matrix, and thus they improve punchability, as a starting point of breaking, like Cr or a Cr compound. However, these elements cause damages to properties required for production, such as casting property or hot working property, and therefore their addition quantity must be strictly controlled.
Pb and Bi are hardly solid-soluble in the Cu matrix, and therefore, the effect on improving punchability is significantly. It is recognized that the effect on improving punchability appears by adding them in amounts of 0.001 wt % or more of Pb and Bi, respectively. However, the manufacturing properties are greatly affected by such addition, and an alloy cannot be normally manufactured if Pb and Bi are added in excess of 0.06 wt %.
An effect on improving punchability appears by adding Ca, Sr, Te, Se, and a rare earth element in quantity of 0.005 wt % or more of Ca, Sr, Te, Se, and a rare earth element, respectively. If these elements are added in excess of 0.1 wt %, the casting property and hot working property are damaged.
Therefore, the adding quantity of one of these elements is controlled as described above, and the total amount of addition of two or more elements is defined to be 0.001 to 0.1 wt %.
Now, Si, contained in a copper alloy according to the third embodiment and fourth embodiment of this invention, will be described.
Si forms a Crxe2x80x94Si compound by its addition in a small amount letting Cr easily precipitate. As a result, the density in number of a precipitation phase A increases, and the punchability is significantly improved. If its content is less than 0.005 wt %, the Crxe2x80x94Si compound is hardly formed. If it exceeds 0.1 wt %, the precipitation phase A excessively increases, the precipitation phase B decreases with this increase, and the strength characteristics are lowered. In addition, the quantity of Si in the solid solution increases, and the conductivity is lowered.
Preferably Si is added to make Cr:Si=3:1 in terms of the ratio of number of atom, so that Si can exist as Cr3Si.
Now, reasons why Si has been particularly selected. from among a number of elements will be described.
According to an object of the present invention, it is required to produce Cr compound by reacting with Cr. Elements for producing Cr compound include P, S, O, Ge, and Pt, as well as Si. Among them, P, S, and O have very strong force in binding with Cr, because they are non-metal elements, and a compound is produced during dissolving and/or casting. Thus, its dispersion state is substantially uncontrollable. In addition, Ge and Pt are hardly dissolved, and they are expensive, so their use is not practical. Because of this, Si was selected, which is most effective in every respect.
In the above-described compound of the present invention, the manufacturing method is important in order to preferably achieve the required characteristics.
According to the present invention, the density in number of the large precipitation phase A, which improves punchability, is controlled to 1xc3x97103 to 3xc3x97105/mm2, by limiting the heat treatment temperature before hot working to 880 to 980xc2x0 C.
Conventionally, in the case of a Cuxe2x80x94Cr-series alloy, the heat treatment temperature before hot working has been in excess of 980xc2x0 C. This is because the above heat treatment was carried out to completely dissolve Cr as a solid solution, and heat treatment was not carried out at a temperature of 980xc2x0 C. or less, at which Cr precipitates.
If the heat treatment temperature is higher than 980xc2x0 C., the density in number of the precipitation phase A of coarse Cr or a Cr compound, of 0.1 to 10 xcexcm in maximum diameter, is lowered, and the punchability is not improved.
Conversely, if the heat treatment temperature is less than 880xc2x0 C., the density in number of the precipitation phase A is excessively high. Thus, the density in number of the precipitation phase B, of 0.001 to 0.030 xcexcm, which precipitates during the subsequent process, is lowered, and the required strength characteristics cannot be obtained.
From such a viewpoint, the heat treatment temperature before hot working is in the range of from 880 to 980xc2x0 C. In particular, the temperature is preferably 910 to 940xc2x0 C.
In the present invention, the density in number of the fine precipitation phase B, which contributes to improving strength characteristics, is controlled to be 10 times or more of that of the precipitation phase A, by limiting the aging treatment temperature to 360 to 470xc2x0 C.
If the aging treatment temperature is less than 360xc2x0 C., the precipitation phase B does not precipitate sufficiently. If the temperature exceeds 470xc2x0 C., the precipitation phase B is coarsened. In any case as well, the required strength characteristics cannot be achieved.
This aging treatment is applied before or after cold working has been carried out following hot working; however, the treatment may be applied during cold working. In this case, it is recommended that annealing be applied at a comparatively low temperature after cold working, and that working strain be reduced.
When the above low-temperature annealing is applied according to batch-type annealing, preferably the annealing is carried out at a temperature of 200 to 400xc2x0 C., for 0.5 to 5 hours. When the above annealing is applied according to running annealing, preferably the annealing is carried out at a temperature of 600 to 800xc2x0 C., for 5 to 60 seconds.
Correction treatment may be carried out by a tension leveler, a roller leveler, or the like, before or after final heat treatment (aging treatment or low-temperature annealing), as required.
As has been described above, according to the copper alloy of the present invention, in the Cu matrix of a Cuxe2x80x94Cr-series alloy, a precipitation phase A of Cr or a Cr compound of 0.1 to 10 xcexcm in maximum diameter, is provided, at a density in number of 1xc3x97103 to 3xc3x97105/mm2, to improve punchability and a precipitation phase B of Cr or a Cr compound of 0.001 to 0.030 xcexcm in maximum diameter, is provided, at a density in number that is 10 times or more of that of the precipitation phase A, to improve strength characteristics. This alloy can be applied to general conductive materials, such as terminal connectors, switches, relay materials, punched by a press, including multi-pin and small pitch lead frames finely punched, thereby ensuring improvement of productivity. In addition, the copper alloy of the present invention can be easily manufactured by subjecting it to heat treatment at a temperature 880 to 980xc2x0 C. before hot working, and subjecting it to aging treatment at 360 to 470xc2x0 C. before or after cold working. Therefore, a significant advantageous effect is achieved from the industrial viewpoint.